In view of the rapid progress in the development of medical techniques in recent years, a variety of medical devices are currently implanted in the living body for a prolonged period. In particular, polymeric materials have been actively developed as materials for implantation in the living body (to be referred to as "implantation material" or "implantation polymeric material" hereinafter), because their mechanical properties are closer to those of biological components than those of metals, ceramics and the like. Polymeric materials can be processed easily and exhibit properties such as anti-thrombogenetic activity, biocompatibility and the like. Of these polymeric materials, elastic materials such as segmented polyurethane are preferably used in artificial blood vessels, artificial hearts, insulation coatings of pacemaker leads and the like because of their excellent mechanical properties and high compatibility with biological tissues.
In spite of these excellent properties as implantation materials, the long-term stability of polymeric materials in the living body is inferior to that of other materials because polymeric materials are apt to decompose or degradate in the living body, thus causing problems such as decrease in the mechanical strength, eluation of decomposed compounds and the like. Also, in the case of elastic, soft or hydrophilic materials, they have flexible polymer chains and, as a result, have a higher possibility of degradation and decomposition in comparison with hard materials. Decomposition and degradation in the living body depends also on the shape of the material and increases when the material has a large surface area. As a consequence, when polymeric materials are made into thin film, porous and similar implantation materials making use of their flexibility, it is highly probable that the degree of the decomposition and degradation of the resulting implants is high.
To date, a method for effectively inhibiting biological decomposition and degradation of polymeric materials has not been found, thus preventing the full utilization of the benefits of polymeric materials.